This invention relates to wound capacitors of the metallized film type, and more particularly to such capacitors in which two separate capacitors or two capacitors with a common place are conveniently fabricated in a single winding.
In U.S. Pat. No. 3,921,041 entitled "Dual Capacitor" which is assigned to the assignee of the present invention, a dual metallized capacitor and the method of making the same is provided. In accordance therewith, first and second dielectric film strips being metallized on one side thereof, are wound in substantially cylindrical form with the non-metallized sides of each strip in contact with the metallized side of the other strip. After winding a predetermined number of revolutions depending upon the capacitance desired, the winding is interrupted and an electrode is advanced against one of the metal layers of the film, a voltage is applied thereto and the winding process is continued which removes the metallic layer leaving a non-metallized intermediate region or gap in one of the metallized layers, the length of which is sufficient to encircle the capacitor section at least once. After formation of the gap, the electrode is removed and a sheet of insulating material, such as plastic, is inserted therein and would with the sheet protruding from one end thereof to form a circular barrier which extends outward from the end of the capacitor so formed. The purpose of the insulated barrier is to separate the two plates on each side of the gap and to permit the making of electrical connections therein without shorting the gap. Accordingly, the two plates of the capacitor to which electrical connections are made are first coated on the ends of the capacitors so formed with a metallized layer to which electrical connections are made both within and outside the barrier. Since the length of the gap encircles the capacitor section at least once, the insulating layer must encircle the gap and requires more than two revolutions to do so. Although the capacitors fabricated using this technique are quite satisfactory, the length of the gap required, along with the amount of insulating material required to be inserted to encircle the gap, tends to slow the winding process as well as requiring use of extra material both with respect to the metallized dielectric film as well as the amount of insulating sheet required to encircle the gap.